SPECIAL WORKS
Surface aerators couldn't mix the tank comprehensively.
Black Waters and Landia end bad odours at paper mill
A new aeration system has rescued a paper mill in El Salvador that was on the brink of $M fines for causing major odour issues.
Changes to environmental regulations had put the company into a crisis situation, despite the fact that they had already installed four 30HP surface aerators in their aeration tank in an attempt to quell the increasingly bad Odor problems.
With the authorities set to take serious punitive measures, the paper mill called in leading wastewater treatment business, Black Waters to see if they could bring about a solution.
“This was a major challenge,” said Roberto Escalante, Principal of Black Waters.
“Nobody in our industry particularly relishes working with a slanted floor (!) rectangular tank (1,000m3), but I can tell you that the twisted face of the paper mill’s CEO was in far more pain than mine!
“It was primitive; in a bad way, resulting in the possibility of substantial fines that caught the paper mill completely off guard,” he added.
“The odors were awful, so we went straight into action with a sludge sampler to see what was going on, in order to establish a proper profile.”
Across the 75.4’ (23m) length tank, which has a shallow end at 6.2’ (1.87m) and a deep end of 13’ (4m), Roberto found that only five of the one-meter sections were free from sediment. The rest ranged from 0.8” to as much as 18” of sediment, varying from light brown towards the shallow end to thick dark grey at the deep end.
“No wonder it stank so much,” added Roberto.
“At the deep end it was septic, because the surface aerators couldn’t mix the tank comprehensively. The slanted tank had become a biological reactor, but with the buildup of sediment, there just wasn’t enough oxygen to allow the bugs to do their job properly. They couldn’t ‘breathe’ and so would die. It was nasty.”
62 | May 2025 |
draintraderltd.com Dire situation very much needed some oxygen
He continued: “All well and good having some mixing, but this dire situation very much needed some oxygen. The wastewater from the paper, which in this case was from a process manufacturing tissue paper, is surprisingly abrasive. Surface aerators can make it appear as if there is lots happening, but underneath the surface it can be a totally different story. In a fairly short space of time, foul odors will soon tell you that something is seriously wrong!”
With a potential $M lawsuit for violations on the horizon, Black Water urgently sought a rapid but long-lasting solution, consulting with contacts in the US and beyond to see what might be available.
“With a slanted tank,” added Roberto, “they all said they wouldn’t blame me if I walked away. But we are engineers of course, so we’ll always want to find an answer, even in this case, where it possibly couldn’t be a perfect world solution.
Guiding post into concrete block assembly for vastly improved aeration.
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